Recently, the use of pre-filled syringes, which are syringes already filled with a drug, has become popular due to their good user-friendliness and in view of preventing medical accidents such as mix-up of drugs (Patent Document 1). The front end portion of a pre-filled syringe to which a needle is to be attached is sealed with a nozzle cap. Prior to injection, the nozzle cap is removed from the front end portion and a needle is attached thereto. A gasket is then slid by pushing a plunger rod toward the front end portion so that the drug is expelled.
For such pre-filled syringes, silicone lubricants are widely used. However, they cannot be used for those intended for biopharmaceuticals and the like because they cause inactivation of these drugs. Therefore, recently, in order to secure the stability of drugs, gaskets laminated with a fluororesin film have been widely used. Since the air-tightness and liquid-tightness of gaskets have an impact on the quality and stability of drugs, the gaskets are required to have high levels of these important properties. However, when used with a glass or resin syringe, gaskets laminated with a fluororesin film problematically exhibit poorer air-tightness and liquid-tightness than conventional, non-laminated rubber ones.
In particular, gaskets produced by laminate molding a skived PTFE film using a conventional mold allow liquid to leak out after sterilized by steam. Even in the case that such a gasket is designed to have an annular protrusion that provides a wider sealing width to improve its sealing performance, the air-tightness and the liquid-tightness are not improved. Moreover, in the approach to increase the annular rib diameter to increase compressibility, some problems may arise such as difficulty in setting the gasket in a syringe and creases on the stacked film around an annular sealing portion of the gasket. Still another problem is high resistance against sliding of a piston. Thus, such approach cannot provide an effective solution.
Patent Document 1: JP 2005-185747 A